/Engine/Source/Editor/UnrealEd/Classes/Editor/EditorEngine.h
Check the InCmdParams for "MAPINISECTION=". If found, fill in OutMapList with the proper map names.
void ParseMapSectionIni ( const TCHAR * InCmdParams, [TArray](API\Runtime\Core\Containers\TArray)< [FString](API\Runtime\Core\Containers\FString) > & OutMapList )